Bone and Body Composition by Dual-Energy X-ray Absorptiometry Across a Spectrum: From Precocious to Physiological Puberty

Background: In recent years, a rising incidence of central precocious puberty (CPP) has been reported, with a notable increase during the COVID-19 pandemic. The onset of puberty is influenced by a multifactorial interplay of genetic, nutritional, environmental, and psychosocial factors. Since puberty is marked by significant changes in body composition and bone mineral accrual, dual-energy X-ray absorptiometry (DXA) represents a valuable tool for accurately assessing fat and lean mass distribution, as well as skeletal development, offering more detailed insights than conventional anthropometric measures. Aim: To evaluate the clinical, auxological, metabolic, and densitometric characteristics of girls with early pubertal development and to explore potential associations with lifestyle factors and body composition. Methods: We conducted a retrospective, single-center study including 184 girls with early breast development (before age 9), referred for suspected precocious puberty between 2011 and 2024. Girls were categorized as having central precocious or early puberty (Group P, n=108) or premature thelarche (Group T, n=76), and were compared with age-matched prepubertal controls (Group C, n=47). Data collection included anthropometric measurements, hormonal and metabolic profiles, pelvic ultrasound, and whole-body DXA scans for the assessment of both body composition and bone mineral status. Participants also completed standardized lifestyle questionnaires (KIDMED, PAQ-C, SDSC, and screen time). Results: Compared to Group T, girls in Group P showed significantly higher delta height-target heigh (ΔH-TH) SDS (p = 0.005), bone age, IGF-1 SDS (adjusted for both chronological and bone age), and uterine dimensions (p < 0.001). In contrast, Group T exhibited significantly higher height SDS, weight, BMI SDS, ΔH-TH SDS (p < 0.05), and IGF-1 SDS (adjusted for both chronological and bone age) compared to Group C (p < 0.001). Additionally, girls in Group P had a significantly lower android-to-gynoid fat ratio and greater total free fat mass than those in Group T (p < 0.05). Compared to controls, girls in Group T showed significantly increased fat and lean mass, as well as higher BMD Z-scores at both the lumbar spine and total body level (p < 0.05). Within Group T, girls presenting with pubarche as the initial pubertal sign had significantly higher weight and BMI SDS (p < 0.001), greater android and gynoid adiposity, total and free fat mass, limb lean mass, , and lumbar spine BMD Z-score than those with thelarche (p < 0.01). In Group T, pubarche-onset girls showed higher Fat-to-Lean Ratio (p < 0.01), indicating greater metabolic risk than those with thelarche. Lifestyle data (n=100) showed: • Low adherence to the Mediterranean diet in 21.7% of Group P and 16.1% of T; • 46.2% reported low physical activity (no difference between groups P and T); • 28% had sleep disturbances (no intergroup difference); • 37.2% exceeded 2 hours/day of screen time, more common in Group P. Conclusions: Significant differences in anthropometry, IGF-1, bone age, and DXA-derived fat and lean mass were observed between groups. Notably, girls with pubarche as the first pubertal sign showed more adverse body composition profiles. Lifestyle data highlighted suboptimal diet, reduced physical activity, and excessive screen use as modifiable risk factors. These findings underscore the importance of early identification, lifestyle interventions, and individualized management to mitigate long-term health risks associated with early pubertal development.